1. Field of the Invention
The invention generally relates to photographic cameras. More particularly, the invention relates to a camera which, when loaded with a light-tight cartridge containing a filmstrip, warns the user of a film take-up malfunction by preventing manual actuation of the shutter release and, when not loaded with the cartridge, permits manual actuation of the shutter release to test-operate the camera.
2. Description of the Prior Art
To load most 35 mm cameras, the film cartridge is inserted in a loading chamber of the camera and the forward end portion of a film leader projecting from a light trapping slit in the cartridge is placed over a film take-up spool in a take-up chamber of the camera. In some cameras, the forward end portion of the film leader is manually attached to the take-up spool before a back door of the camera is closed. Then, an initial film winding operation is performed, for example, by pivoting a winding lever and depressing a shutter release button several times until the entire leader is wound onto the take-up spool and the first frame area of the filmstrip is positioned for exposure. In other cameras, the forward end portion of the film leader is automatically secured to the take-up spool at the beginning of the initial film winding operation. As the take-up spool is rotated, one or more circumferential teeth on the spool engage the forward end portion of the film leader in its perforations to wind the leader onto the spool and to position the first frame area of the filmstrip for exposure. A spring-like deflector or other suitable means may be provided on the back door of the camera for pressing the film leader against the take-up spool to facilitate engagement of the forward end portion of the leader by the teeth on the spool. After the first frame area of the filmstrip is exposed, subsequent exposures are made by repeating the film winding and shutter releasing operations.
A problem that exists in some 35 mm cameras as a consequence of the loading procedure is that, even though the user believes the forward end portion of the film leader is secured to the take-up spool, the forward end portion may fail to be engaged with the spool or may disengage from the spool during the initial film winding operation. As a result, the film leader will not be wound onto the take-up spool and the first frame area of the filmstrip cannot be positioned for exposure. However, since the back door of the camera is closed, the user may not become awary of the film take-up malfunction because the winding lever and the shutter release button can be manually operated in the usual way. The user, thus, under the delusion that the camera is working properly might begin photographing and would learn of the malfunction only when the back door of the camera is re-opened to remove the cartridge from the camera, thereby possibly losing certain picture opportunities.
A prior art solution to the problem is proposed in U.S. Pat. No. 3,665,830 granted May 30, 1972 to Maeda. In the Maeda patent, when a film cartridge is not loaded in the camera, the winding lever and the shutter release button can be manually operated in the usual way to test-operate the camera. This is desirable in order to demonstrate the camera to a customer in a store and to check the camera during manufacture. When a film cartridge is loaded in the camera, the shutter release button is locked, but the winding lever can be pivoted several times to wind the film leader onto the take-up spool and to position the first frame area of the filmstrip for exposure. The shutter release button is unlocked only in response to the occurrence of two events. First, a sensing lever normally in contact with the take-up spool is displaced from the spool by the first convolution of the film leader being wound onto the spool. Then, a counter dial is rotated to a position which indicates that the first frame area of the filmstrip is positioned for exposure. Thus, in the Maeda patent, there is disclosed a camera which, when loaded with a film cartridge, warns the user of a film take-up malfunction by preventing manual actuation of the shutter release button and, when not loaded with the cartridge, permits manual actuation of the shutter release button to test-operate the camera. However, this capability in the Maeda patent is achieved only by a relatively complex assemblage of a number of cams, levers and springs which significantly adds to the cost of manufacture of the camera and increases the possibility of a mechanical break-down.